Drive arrangement for three wheeled vehicles

ABSTRACT

A three wheeled shaft driven off the road vehicle having an improved driving arrangement. The driving arrangement includes an overload release coupling that is positioned between the driven gear and a drive shaft that drives the rear wheels so as to minimize the complexity of the transmission and to protect the engine and drive. A trailing arm rear suspension is employed that has widely spaced bearings for rotatably journaling the rear axle to minimize unit loadings. An arrangement is also disclosed for facilitating axial positioning of the driven gear on the output shaft without necessitating the use of shims.

BACKGROUND OF THE INVENTION

This invention relates to three wheeled vehicles and more particularlyto an improved drive arrangement for such vehicles.

Three wheeled vehicles presently enjoy large popularity for off the roaduse. Such vehicles normally include a steerable front wheel and a pairof driven rear wheels. Large low pressure tires are mounted on all ofthe wheels to facilitate use in a wide variety of terrains. Because oftheir off the road use, these vehicles are subjected to considerablestress. Because they are operated off the road, however, they should bereadily durable so that they will not fail in a remote location. Onearea where such units are highly stressed is in the mounting and drivingarrangement for the rear wheels.

It is, therefore, a principal object of this invention to provide animproved arrangement for supporting the rear wheels of a three wheeledvehicle.

It is another object of this invention to provide an axle arrangementfor a three wheeled vehicle wherein the unit loading is substantiallyreduced from prior art devices.

Again, because of the extreme use to which off the road three wheeledvehicles is put, it is important to provide some device for preventingdamage to the transmission and/or engine under extreme conditions.Although it has been proposed to employ an overload release mechanism inthe drive train of a vehicle so as to minimize such damages, theoverload release devices previously proposed have resulted in increasedcomplexity of the drive train and/or transmission

It is, therefore, a still further object of this invention to provide animproved driving arrangement for a three wheeled vehicle.

It is a further object of this invention to provide a three wheeledvehicle drive arrangement that embodies an improved, simplified overloadrelease mechanism.

In many types of arrangements, it is desirable and necessary to provideaccurate location for the axial position of a rotating element. Forexample, in bevel gear drives or similar gearing arrangements, the axialposition of the gears to maintain the proper meshing relationship iscritical. It is normally the practice to employ shims for adjusting theaxial position of the gears. The use of shims for this purpose not onlycomplicates assembly, but also presents problems during servicing.

It is, therefore, a further object of this invention to provide animproved and simplified arrangement for axially locating a rotatingelement.

It is a further object of this invention to provide an improved andsimplified arrangement for maintaining the desired relationship betweena pair of meshing gears.

SUMMARY OF THE INVENTION

A first feature of this invention is adapted to be embodied in atransmission for a three wheeled vehicle or the like comprising a frame,a front wheel dirigibly carried by the frame, a pair of rear wheelscarried by the frame, an engine carried by the frame, and a transmissionthat transmits the drive from the engine to the rear wheels. Inaccordance with this feature of the invention, the engine is positionedwith its output shaft extending parallel to the axis of rotation of therear wheels. The transmission has a primary shaft and a secondary shafteach of which carry intermeshing gears for changing the speed ratiobetween the primary and secondary shafts. The transmission shafts havetheir rotational axes extending parallel to that of the rear wheels.Means are provided for driving the primary shaft from the engine outputshaft. A drive shaft is incorporated for driving the rear wheels andwhich extends generally perpendicular to the axis of rotation of therear wheels. Means including an overload release device drive the driveshaft from the transmission secondary shaft.

Another feature of the invention is adapted to be embodied in a threewheeled vehicle or the like having a frame, a front wheel dirigiblysupported by the frame, trailing arm means consisting of a pair ofspaced apart arm members that are pivotally supported on the frame atone end and which rotatably support an axle at their other end. A pairof rear wheels are affixed for rotation with the axle and power meanscarried by the frame drive the axle. In accordance with this feature ofthe invention, the trailing arm means carry a pair of spaced apartbearing members for journaling the axle in proximity to the rear wheelsfor minimizing unit loading thereupon.

Another feature of this invention is adapted to be embodied in anarrangement for obtaining and maintaining a predetermined axial locationfor a rotating member. This arrangement includes bearing means thatdefine an axis of rotation of the member and deformable spacer meansinterposed between the bearing means and the member for determining therelative position therebetween. Means are provided for effectingmovement of the rotatable member relative to the bearing means forpermanently deforming the deformable member to establish the finalposition of the rotating member relative to the bearing means.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view of a three wheeled vehicle constructedin accordance with an embodiment of the invention, with portions of thevehicle shown in phantom.

FIG. 2 is a top plan view of the rear portion of the vehicle, withcertain components deleted and with other components shown in phantom.

FIG. 3 is a further enlarged top plan view, with portions broken away,other portions shown in section, and still further portions shownschematically, showing the engine, transmission and rear wheelsuspension.

FIG. 4 is an enlarged cross-sectional view taken along the line 4--4 ofFIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A three wheeled vehicle constructed in accordance with this invention isidentified in the drawings generally by the reference numeral 11. Thevehicle 11 includes frame means, which in the illustrated embodimentcomprises a tubular frame assembly, indicated generally by the referencenumeral 12. When the term "frame means" is used in this specificationand in the claims, it is intended to include any of the known type offrame structures including unitary or so-called frameless constructions.

The frame 12 consists of a head pipe 13, a main tube 14 and a pair ofdown tubes 15. The down tubes 15 are reversely bent at their lower endsand these ends are affixed, in a manner to be described, to upstandingseat pillar tubes 16. The down tubes 15 and seat pillar tubes 16 resultin a frame of what is known as the double cradle construction. A pair ofseat rails 17 are affixed to the seat pillar tubes 16 adjacent theirpoint of connection with the main tube 14 and extend rearwardly. Theseat rails 17 are supported contiguous to their trailing ends by meansof a pair of back stays 18 that extend from the seat pillar tubes 16 andwhich are affixed thereto and to the seat rails 17.

A body, of any known type, is supported on the frame assembly 12 in aknown manner. Since the body forms no portion of the invention, it hasbeen shown only in phantom and is identified generally by the referencenumeral 19. The body 19 in turn supports a seat 21.

A front fork assembly 22 is journaled by the head pipe 13 in a knownmanner. A front wheel, mounting a tire of the balloon low pressure type23, is suitably jounrnaled at the lower end of the fork assembly 22. Ifdesired, the fork assembly 22 may employ a suspension device forpermitting suspension movement of the wheel 23 relative to the frameassembly 12. In addition, the wheel 23 may be steered by means of ahandlebar assembly 24 that is affixed to the fork 22 in a known manner.

A pair of rear wheels carry balloon, low pressure tires 25. The rearwheels are affixed in a suitable manner to a rear axle 26, which axleis, in turn, journaled in a manner to be described by a trailing armassembly, indicated generally by the reference numeral 27. The trailingarm assembly 27 in addition to rotatably supporting the axle 26 supportsthe axle 26 and rear wheels including the tires 25 for suspensionmovement relative to the frame assembly 12. The manner in which this isdone will become more apparent as this description proceeds.

The trailing arm assembly 27 includes a pair of transversely spacedapart arm members 28 and 29. The arm members 28 and 29 compriserespective forward tubular parts 31 and 32. The parts 31 and 32 have agenerally open configuration and for a reason to be described, the part31 is substantially larger than the part 32. The forward ends of thetubular parts 31 and 32 are affixed to a tubular cross tube 33. Thecross tube 33, in turn, carries spaced bearings 34 at its opposite endswhich rotatably support the trailing arm assembly 27 at its forward endon a pair of stub shafts 35. The stub shafts 35 are, in turn, carried bybracket plates 36 which are affixed, as by welding, to the down tubes 15and seat pillar tubes 16 and which brackets also connect these tubes.The stub shafts 35 are held in assembled relationship by cap screws 37.Upon removal of the screws 37, the trailing arm assembly 27 andsupported wheels and tires 25 may be removed as a unit from the vehicle11 for servicing.

It should be noted that the bearings 34 are spaced transversely apart ata substantial distance so as to lend stability to the vehicle 11.Preferably, the bearings 34 are disposed closely adjacent the outer sideperiphery of the vehicle 11. In a like manner, the arm members 28 and 29are spaced apart a substantial transverse distance, for a reason to bedescribed.

A final drive housing assembly, indicated generally by the referencenumeral 38, is provided at the rear end and form a part of the trailingarm assembly 27. The final drive housing assembly 38 comprises a mainmember 39 having a tubular portion that defines a transversely extendingopening 41. At one side, the member 39 is provided with a forwardlyextending projection 42 that forms a portion of the arm member 29. Thetubular portion 32 is provided with an outstanding flange 43 that isaffixed to the forward end of the portion 42 by means of studs 44 andnuts 45. Locating surfaces 46 of the studs 44 cooperate with machinedopenings in the flange 43 so as to permit alignment.

A final drive cover member 47 is affixed to the member 39 by means of aplurality of screws 50. The cover 47 has a forwardly extending portion48 which forms a part of the arm member 28. A sleeve 49 istelescopically received in the tubular member 31 and is affixed to it,as by welding. The sleeve 49 has an outwardly extending flange 51 thatis affixed to the cover member projection 48 by means of studs 52 andnuts 53. The flange 51 has machined openings 54 that cooperate with thestuds 52 so as to locate the tubular sleeve 49 accurately relative tothe final drive cover member 47.

On the side adjacent the arm member 29, the final drive housing 39supports a bearing 55. The bearing 55 is positioned adjacent the outerperiphery of the housing 39 and in relatively close proximity to theadjacent wheel 25. In a similar manner, the final drive cover member 47carries a bearing 56 adjacent its outer periphery and in relativelyclose proximity to the adjacent wheel 25. The bearings 55 and 56rotatably journal the rear axle 26 at widely transversely spaced points.Because of this wide spacing, the loads exerted on the bearings 55 and56 by the axle 26 will have little bending moment and unit loadings willbe substantially reduced from constructions wherein the rear axlebearings are more closely spaced to each other. Suitable seals 57, 58are carried outwardly of the bearings 55, 56, so as to protect thebearings 55, 56 and the associated components of the final drive, whichare to be described.

It should be readily apparent that the trailing arm assembly 27 supportsthe rear wheels and tires 25 for pivotal movement relative to the frame12 about a transversely extending axis, defined by the bearings 34, uponsuspension travel. A suspension element, indicated generally by thereference numeral 59, is provided for controlling this suspensiontravel. The suspension element 59 may be of any known type andpreferably comprises a combined shock absorber and enclosed coil springarrangement. One end of the suspension element 59 is pivotally connectedto the frame main tube 14 by means of a bracket 61 and pivot pin 62. Theopposite end of the suspension element 59 is connected pivotally to abracket 63 that is affixed to the final drive housing 39 in a suitablemanner, as by welding. The pivotal connection between the suspensionelement 59 and the bracket 63 is provided by means of a pivot pin 64.

An internal combustion engine, which may be of any known type, indicatedgenerally by the reference numeral 65, is supported within the frameassembly 12 in a manner to be described. The engine 65 includes acombined crankcase transmission assembly 66. As may be seen in FIG. 4, apair of cross tubes 67 and 68 extend between and are affixed to the seatpillar tubes 16 and down tubes 15, respectively. Brackets 69 areaffixed, as by welding, to the cross tubes 67. A bolt assembly 71extends through and is affixed to the brackets 69 and passes through acylindrical opening in a boss formed on the engine crankcase andtransmission assembly 66 so as to provide a partial support for theengine 65. In a like manner, a pair of brackets 72 are affixed to thecross tube 68. A bolt assembly 73 extends through a similar opening in aboss formed in the lower portion of the transmission crankcase assembly66 so as to provide further support for the engine 65. Forward brackets74 and 75 are also affixed to the frame assembly 12 for supporting theforwardmost portion of the engine 65 in a suitable manner.

Referring now primarily to FIG. 3, the engine 65 and the transmissionassociated with the crankcase transmission assembly 66 is illustratedschematically. In this schematic illustration, the engine 65 is depictedas being of the single cylinder type including a cylinder 76 in which apiston 77 is supported for reciprocation. The piston 77 is connected bya piston pin to one end of a connecting rod 78. The other end of theconnecting rod 78 is journaled upon a throw of a crankshaft 79 that issupported in the crankcase 66 on suitable bearings for rotation about anaxis that extends transversely of the vehicle 11 and parallel to theaxis of rotation of the rear axle 26. The crankshaft 79 drives a clutch(not shown) which, in turn, drives a transfer gear 81. The transmission66 includes a primary shaft 82 and a secondary shaft 83. The primary andsecondary shafts 82, 83, are journaled in suitable bearings and havetheir axes of rotation extending parallel to that of the crankshaft 79and also that of the rear axle 26. Hence, the shafts 79, 82, 83 and axle26 all rotate about parallel axes.

An input transfer gear 84 is affixed to the primary shaft 82 and is inmesh with the crankshaft driven transfer gear 81 so as to drive theprimary transmission shaft 82 from the crankshaft 79 through theaforenoted clutch. A plurality of gear sets 85, 86 and 87 consisting ofdriving gears that are affixed to the primary shaft 82 and driven gearsthat are journaled upon the secondary shaft 83 are provided in thetransmission 66. As is well known, the driven gears of the gear sets 85,86 and 87 may be selectively coupled to the secondary shaft 83 so as toprovide a speed change driving relationship between the primary andsecondary shafts 82, 83.

The rotatable support for the secondary shaft 83 includes a bearing 88that is supported within the casing of the crankcase transmissionassembly 66 and which is disposed in proximity to an output shaft cavity89 formed in this casting. A bevel gear 91 is rotatably coupled to thesecondary shaft 83 within the cavity 89. The bevel gear 91 is in meshwith a driven bevel gear 92 that is journaled on an output shaft 93. Theoutput shaft 93 is, in turn, journaled by a pair of spaced bearings 94and 95 for rotation about an axis that extends perpendicularly to theaxis of the transmission secondary shaft 83. As a result, the shaft 93is also perpendicular to the axis of rotation of the crankshaft 79, theaxis of the transmission primary shaft 82 and the axis of rotation ofthe rear axle 26.

An overload release device, indicated generally by the reference numeral96, couples the driven bevel gear 92 to the output shaft 93 forsimultaneous rotation. The overload release device 96 comprises a firstannular sleeve 97 that is coupled, by means of a splined connection, forsimultaneous rotation with the output shaft 93 contiguous to the bearing95. A second sleeve 98 is also splined to the output shaft 93 and ispositioned in proximity to the bevel gear 92. A coil compression spring99 is interposed between the sleeves 97, 98, and urges a plurality ofprojections 101 formed on one end of the sleeve 98 into engagement withcorresponding recesses 102 of the bevel gear 92. As a result of thisinterengagement, the bevel gear 92 is rotatably coupled to the sleeve 98and, in turn, to the output shaft 93. In the event an obstruction torotation of the axle 26 of sufficient magnitude is encountered, theprojections 101 will be cammed out of the bevel gear recesses 102 tocompress the spring 99 and discontinue the driving relationship betweenthe bevel gear 92 and the sleeve 98. Immediately upon removal of theobstruction, the spring 99 will cause the projections 101 to reengagethe recesses 102 and reestablish the driving relationship.

As is well known, it is important to establish the desired relationshipbetween bevel gears 91 and 92 so as to insure a good drivingrelationship, minimize wear and noise. Normally, this adjustment hasbeen effected through the use of shims interposed between the bevel gearand its supporting components. Of course, the use of such shims providesmanufacturing difficulties and furthermore can present problems whenservicing the transmission. In accordance with this invention, anarrangement is provided that achieves an automatic adjustment of themeshing relationship and its maintenance during operation and whenservicing.

A deformable spacer member, indicated generally by the reference numeral103 is interposed between the inner race of the bearing 95 and ashoulder 104 formed on either the shaft 93, sleeve 97 or as a separatemember that is coupled to the shaft 93. The shaft 93 has, at its lefthand end as viewed in FIG. 3, an outwardly extending flange 105 thatengages a sleeve 106 against which the bevel gear 92 is abuttinglyengaged. By moving the shaft 93 axially to the right as seen in FIG. 3,the meshing relationship between the gears 91 and 92 may be established.During this movement, the deformable spacer 103 will be permanentlydeformed until the desired axial position is reached. Thereafter, thedeformable sleeve 103 will be held in its permanently deformed conditionand will maintain the spacing between the gears 91 and 92.

In order to couple the shaft 93 to an output member and to achieve theaxial deformation of the spacer 103, there is provided a connection to auniversal joint 107, which will now be described. The universal joint107 has an input yoke 108 that has internal splines 109 to provide adriving connection with corresponding splines on the output shaft 93.Means including a nut and washer assembly 111 are threaded onto athreaded end of the output shaft 93 so as to engage the input yoke 108.The input yoke 108 has an inwardly extending shoulder that engages theinner race of the bearing 95. Hence, tightening of the nut 101 willeffect axial movement of the shaft 93 to the right as viewed in thisfigure. This movement will be transmitted, as aforenoted, to move thebevel gear 92 and also so as to deform the deformable spacer 103. Whenthe appropriate position is reached, as may be sensed by the torquenecessary to tighten the nut 101, the preestablished meshingrelationship will be established and further tightening of the nut 111is discontinued.

The universal joint 107 is positioned within a hollow interior 112 ofthe tubular member 31 and is disposed so that its pivot axis is alignedwith the pivot axis of the trailing arm assembly 27 as defined by thebearings 34. The forward end of the tubular member 31 extends forwardlyof the cross tube 33 and is generally opened. A flexible boot 113encircles this open end and is sealed to the transmission crankcaseassembly 66 so as to protect the internal components including the area112 and the universal joint 107.

The universal joint 107 has an output yoke 114 that has a splinedconnection 15 to a drive shaft 116 that extends axially through thetubular member 31 and the tubular sleeve 49 into proximity with thecover 47 of the final drive assembly. The drive shaft 116 has anexternally splined rear end portion 117. The splined portion 117 isreceived within a corresponding female splined portion 118 of a driveyoke 119. The drive yoke 119 is affixed for rotation with a splinedshaft 121 of a final drive pinion 122. A nut 123 affixes the yoke 119 tothe pinion 122. A coil spring 124 is received within an internal openingof the drive shaft 116 so as to urge the drive shaft 116 in a generallyforward direction.

The pinion 122 is rotatably journaled in the final drive cover 47 bymeans including a ball bearing 125 and a roller bearing 126, whichbearings are positioned on opposite sides of the pinion 122. The pinion122 meshes with a ring gear 127 that is affixed in a suitable manner toa hub 128. The hub 128 is, in turn, rotatably supported by a pair ofspaced bearings 129, 131, that are carried in the housing assembly 39and cover plate 47, respectively. The hub 128 has a splined connection132 to the axle 26 so as to effect a driving connection between the ringgear 127 and the axle 26.

The engine 65 is provided with a suitable induction system forintroducing a fuel/air mixture to the cylinder 76. In addition, anexhaust system including an exhaust pipe 133 extends from a forwardlyfacing exhaust port to one side of the vehicle 11 and terminates at acombined muffler exhaust pipe 134 that discharges rearwardly.

A braking system may be provided for the rear axle 26 which can includea brake rotor or disc 135 (FIG. 3) that is affixed to a splined portion136 of the rear axle 26 on the side opposite the ring gear 127. Asuitable brake caliper (not shown) can operate with the brake disc 135to provide braking in a known manner. Of course, various other brakearrangements may be employed.

It should be readily apparent that operation of the engine 65 causes thetransmission 66 to be selectively driven through the clutch and at theappropriate speed ratio chosen by selection of the respective gears 85,86, 87. The transmission secondary shaft 83 then drives the drive shaft93 through the bevel gears 91, 92. This drive is transmitted through theuniversal joint assembly 107 to the pinion gear 122, which, in turn,drives the ring gear 127, rear axle 26 and wheels and associated tires25. During suspension movement, the trailing arm assembly 27 will pivotabout the pivot axis defined by the bearings 34. The universal joint 107permits such suspension movement without affecting the drivingrelationship. In the event an obstruction to turning of the wheels 25 ofsufficient magnitude is encountered, the overload release device 96 willyield so as to prevent any damage to either the transmission 66, finaldrive, or the engine 65. This overload release mechanism willautomatically reengage once the load is removed.

It should be readily apparent that the aforenoted construction providesrelatively low unit loading on the rear axle 26 and its supportingbearings 55, 56, due to the extreme outboard location of these bearings.In addition, a relatively simplified arrangement is provided wherein anoverload release device is incorporated between the transmission and thefinal drive without necessitating the provision of additional shafts anddrives for them to accommodate such an overload release device.Furthermore, a simplified and improved arrangement is provided foraxially locating a rotating element, such as a bevel gear that obviatesthe necessity for using shims or the like.

Although an embodiment of the invention having a preferred constructionhas been disclosed, various changes and modifications may be madewithout departing from the spirit and scope of the invention, as definedby the appended claims.

I claim:
 1. In a transmission for a vehicle or the like comprising framemeans, at least one front wheel dirigibly carried by said frame means, apair of rear wheels carried by said frame means, an engine carried bysaid frame means, and a transmission carried by said frame means, theimprovement comprising said engine being positioned with its outputshaft extending parallel to the axis of rotation of said rear wheels,said transmission having a primary shaft and a secondary shaft eachcarrying intermeshing gears for changing the speed ratio between saidprimary and said secondary shafts, said transmission shafts having theirrotational axes extending parallel to the rotational axis of said rearwheels, means for driving said primary shaft from said engine outputshaft, a drive shaft for driving said rear wheels and extendinggenerally perpendicular to the axis of rotation of said rear wheels,means for driving said drive shaft from said transmission secondaryshaft and an overload release device in the driving connection betweensaid transmission secondary shaft and said rear wheels and remotely fromthe transmission secondary shaft.
 2. In a transmission as set forth inclaim 1 wherein the means for driving the drive shaft from thetransmission secondary shaft comprises a driving gear affixed to thetransmission secondary shaft and a driven gear associated with the driveshaft, the overload release device being positioned between the drivengear and the rear wheels.
 3. In a transmission as set forth in claim 2wherein the overload release device is positioned between the drivengear and the drive shaft.
 4. In a transmission as set forth in claim 3wherein the overload release device comprises positively engagingelements on the driven gear and the drive shaft and biasing means forurging said positively engaging elements into engagement and forpermitting release of the driving engagement therebetween upon anoverload condition.
 5. In a transmission as set forth in claim 1 whereinthe means for carrying the rear wheels by the frame means comprisessuspension means for permitting suspension travel of the rear wheelsrelative to the frame means.
 6. In a transmission as set forth in claim5 wherein the suspension means comprises a trailing arm constructionpivotally connected at one end thereof to the frame means and carryingan axle at the other end thereof to which the rear wheels are affixed.7. In a transmission as set forth in claim 6 wherein the trailing armmeans comprises a pair of spaced apart arm members, at least one of saidarm members being hollow and passing the drive shaft therethrough, therebeing a universal joint in the drive shaft continguous to the pivotalaxis of the trailing arm member.
 8. In a transmission as set forth inclaim 7 wherein the means for driving the drive shaft from thetransmission secondary shaft comprises a driving gear affixed to thetransmission secondary shaft and a driven gear associated with the driveshaft, the overload release device being positioned in the connectionbetween the driven gear and the rear wheels.
 9. In a transmission as setforth in claim 8 wherein the overload release device is positioned inthe connection between the driven gear and the drive shaft.
 10. In atransmission as set forth in claim 9 wherein the overload release devicecomprises positively engaging elements on the driven gear and the driveshaft and biasing means for urging said positively engaging elementsinto engagement and for permitting release of the driving engagementtherebetween upon an overload condition.
 11. In a transmission as setforth in claim 8 wherein the trailing arm means arm members aretransversely spaced apart at a relatively substantial distance, the axlebeing rotatably supported by the trailing arm means by means of a pairof bearing members transversely spaced apart at substantially the widthof the trailing arm means.
 12. In a transmission as set forth in claim11 wherein the overload release device is positioned in the connectionbetween the driven gear and the drive shaft.
 13. In a transmission asset forth in claim 12 wherein the overload release device comprisespositively engaging elements on the driven gear and the drive shaft andbiasing means for urging said positively engaging elements intoengagement and for permitting release of the driving engagementtherebetween upon an overload condition.
 14. In a transmission as setforth in claim 6 wherein the trailing arm means includes a pair ofwidely transversely spaced bearing means rotatably supporting said rearaxle.
 15. In a transmission as set forth in claim 14 wherein the bearingmeans comprises a pair of spaced antifriction bearings positioned at theouter periphery of the rear end of the trailing arm means.
 16. In atransmission as set forth in claim 15 wherein the trailing arm meanscomprises a pair of transversely spaced apart trailing arm members. 17.In a transmission as set forth in claim 1 wherein the overload releasedevice comprises positively engaging elements and biasing means forurging said positively engaging elements into engagement and forpermitting release of the driving engagement therebetween upon anoverload condition.
 18. In a transmission as set forth in claim 1wherein the rear wheels are nonrotatably affixed to an axle, the meansfor driving the rear wheels comprising meshing gears drivinglyconnecting the drive shaft to said axle.
 19. In a transmission as setforth in claim 18 wherein the meshing gears comprise a ring and piniongear.
 20. In a transmission as set forth in claim 19 wherein the ringgear is drivingly coupled to a sleeve, the rear axle being in splinedengagement with said sleeve for driving said rear axle and said sleevein unison.
 21. In a transmission as set forth in claim 20 furtherincluding spaced apart bearing means for journaling said sleeve forrotation.
 22. In a transmission as set forth in claim 21 wherein thespaced apart bearing means are disposed on opposite sides of the ringgear.
 23. In a transmission as set forth in claim 22 further including ahousing for encircling the meshing gears and having a cover plate, oneof the bearing means being carried by said cover plate and the other ofsaid bearing means being carried by said housing.
 24. In a transmissionas set forth in claim 1 further including a tubular housing enclosingthe drive shaft.
 25. In a transmission as set forth in claim 24 furtherincluding a flexible boot interposed between one end of said tubularhousing and the transmission casing.
 26. In a transmission as set forthin claim 25 further including a universal joint drivingly coupling thedrive shaft to the transmission secondary shaft.
 27. In a transmissionas set forth in claim 1 wherein the drive shaft is drivingly coupled toa bevel gear at its input end for driving connection to the transmissionsecondary shaft and a bevel gear at its output end for driving the rearwheels.
 28. In a transmission as set forth in claim 27 further includinga universal joint drivingly connecting one of the bevel gears to thedrive shaft.
 29. In a transmission as set forth in claim 27 wherein theoverload release device is interposed between one of the bevel gears andthe drive shaft.
 30. In a transmission as set forth in claim 29 whereinthe overload release device comprises positively engaging elements andbiasing means for urging said positively engaging elements intoengagement and for permitting release of the driving engagementtherebetween upon an overload condition.
 31. A transmission as set forthin claim 7 further including a single suspension element interposedbetween the trailing arm means and the frame means for controlling themovement therebetween.
 32. A transmission as set forth in claim 31wherein the single suspension element comprises a tubular shock absorberand a coil compression spring.
 33. A transmission as set forth in claim32 wherein the line of action of the tubular shock absorber is disposedin a substantially horizontal direction.